Chapter 6
Using the Shell and Text
Files
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Objectives
In this chapter, you will:
• Describe how a Linux shell operates
• Customize your shell environment
• Use common text editors to create or modify text
files
• Describe popular text-processing methods and
tools used on Linux
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Valued Gateway
Client:
Understanding the Shell
• Command interpreter: program that accepts input
from the keyboard and launches commands or
otherwise controls the computer system
• Linux command interpreter is called the shell
• The shell is only loaded when a user logs in at a
text mode login prompt
• Different types of shells are available for Linux
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Valued Gateway
Client:
The Shell Prompt
• Shell prompt: set of words or characters
indicating that the shell is ready for commands
• The default shell prompt includes four
components:
–
–
–
–
The user account name
The hostname
The last part of the full directory path
A prompt character
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A Standard Shell Prompt
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Client:
The Functions of a Shell
• A shell’s primary purpose is to launch programs
• A Linux shell gives users the ability to write
scripts that the shell can execute
• The shell has many built-in features to work with
files and commands on a Linux system
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Different Types of Shells
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Different Types of Shells
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Valued Gateway
Client:
Entering Commands
• Modern shells include features designed to
simplify the process of entering commands and
command parameters:
– Tab completion
– History feature
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Valued Gateway
Client:
Using Tab Completion
• Tab completion is a shell feature that lets you
enter part of a file or directory name, press the
Tab key, and have the shell fill in the remainder of
the name
• Using tab completion makes it easier to enter
long or complex directory paths and filenames
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Valued Gateway
Client:
Using the History Feature
• Command history: records each command that
you enter at the shell prompt
• History list: recently entered commands
• To locate a previously executed command
– Use the history number
– Use the beginning of a command
– Search the history list
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Client:
The Shell Start-up Process
• The profile scripts are executed when a user logs
into a Linux system
• Additional scripts are executed when a user
starts a shell
• The /etc/profile script contains configuration
information that applies to every user on the
system
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A Typical Start-up Script
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Valued Gateway
Client:
Customizing the Shell
• You can customize the Linux environment with
the following methods:
– Use aliases
– Use symbolic links
– Use environment variables
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Valued Gateway
Client:
Using Aliases
• Alias: string of characters that is substituted for
another string of characters at the shell prompt
• The alias command lets you define an alias for
text you enter at a shell prompt
• General format of the alias command:
alias<string entered>=<string substituted by the
shell>
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Client:
Symbolic Links
• Symbolic link
– File that refers to another file or directory, rather
than containing data itself
– Used when the same data must be accessed from
two locations in the directory structure, or by two
different names
– Commonly used in directories such as /lib and
/usr/lib
• To create a symbolic link, use the ln command
with the -s option
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A Symbolic Link
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Viewing a Symbolic Link
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Client:
Environment Variables
• Environment variables are settings, or values,
available to any program launched by a user
• Each environment variable is assigned a value
• Set command: displays a list of all environment
variables defined in your current environment
• To see the value of an environment variable,
execute echo followed by the environment
variable name preceded by a dollar sign
• The export command makes an environment
variable available to other programs launched
from that environment
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Client:
Using Text Editors
• Linux supports numerous text editors
• Linux system administrator can modify
configuration files using any text editor
• Files that use a markup language can be created
in any text editor
• You can filter text files within some text editors
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Valued Gateway
Client:
The Variety of Linux Text Editors
• Graphical text editors are included on modern
Linux desktops, such as
– gedit in Gnome
– kedit and kate in KDE
• Widely used text-mode editors:
–
–
–
–
vi
emacs
pico
joe
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The pico Text Editor
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Using the vi Editor
• vi is a modal editor – keystrokes are interpreted
differently depending on the mode you are
working in
• vi has several modes:
– Command mode
– Insert mode
– Replace mode
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Using the vi Editor
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vi Commands to Enter Insert or
Replace Mode
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Additional vi Commands
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Text Processing
• There are two methods to create formatted
documents:
– Graphical, or WYSIWYG (what-you-see-is-whatyou-get)
– Rely on markup languages to define special codes
that format documents
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Valued Gateway
Client:
Markup Languages
• Widely used markup languages in the Unix and
Linux world:
– HTML (hypertext markup language)
– TeX – a document-processing system with two
popular versions: LaTeX and TeTeX
– roff codes for online documents
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An HTML Document in vi
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Controlling Fonts
• The X Window System is installed with many
different fonts
• xfontsel graphical program is used to review and
select fonts
• Both Gnome and KDE provide a standard font
selection dialog box
• Fonts are managed in X using the xfs font server
• New fonts can be added to the Linux system any
time
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The xfontsel Program
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The Font Selector Dialog Box
in Gnome
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Valued Gateway
Client:
Manipulating Text Files
• Filtering is the process of adding, removing, or
altering data in the text file based on complex
rules or patterns
• sort command: sorts all of the lines in a text file,
writing them out in alphabetical order
• sed command: processes each line in a text file
according to a series of command-line options
• awk and perl programming languages can be
used to create scripts for filtering text files
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Linux Text-filtering Commands
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Summary
• Linux shell: program that launches other
programs and works with files in Linux
• Modern shells include features designed to
simplify the process of entering commands - tab
completion and history
• Aliases within a shell cause the shell to replace
text on a command-line entry with different text
before trying to execute the command
• Environment variables store values that any
program can access
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Summary
• Linux supports text editors, such as vi
• Linux programs format text using a WYSIWYG
display or markup languages such as LaTeX and
roff use codes
• Fonts are managed in X Windows System using a
font server
• Gnome and KDE provide a dialog box to select
the font for graphical programs
• Filtering text files can be done within some text
editors or using different command-line utilities
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